But they both appeared to stem from seemingly minor incidents — construction workers using parking spaces in his Seattle neighborhood and a woman in his Fort Worth apartment complex who made too much noise.

His father told police in Seattle his son had "anger-management issues," blaming his son's traumatic experiences attempting to rescue victims at the scene of one of the 9/11 terrorist attacks, according to the Washington Post.

"Those events disturbed him," officers said in the police report filed following the Seattle incident.

What caused Alexis to go on Monday's deadly shooting spree in the nation's capital remained a mystery to FBI and Navy officials.

Alexis, who was about to start work at the Navy Yard as a civilian IT contractor, was shot dead in a gunbattle with DC police after shooting at least 12 people dead and wounding eight more.

Navy officials described a pattern of misconduct that led to his discharge after four years of service in the Navy Reserves.

But acquaintances painted a completely different picture, describing him in interviews as a quiet, practicing Buddhist who spoke Thai, traveled widely for work and was taking an online course in aeronautics.

Many said there was "no way" he would carry out such an attack.

"He's not aggressive," Nutpisit Suthamtewakul, a friend and owner of Happy Bowl Thai in White Settlement, Texas, told ABC News. "He had a gun but that doesn't mean he's gonna shoot people. He had a concealed-weapons permit."